Fixes for grid_check random event.

There was an issue, when APC with removed cell in area was powered at power_restore() proc, making area allways powered despite APC was not working.
Removed part of code which unpowers area directly, bypassing the APC process code. This makes grid_check event less laggy and smooth. Downside is lights not being shut down immediatly.
AI SMES still not being affected after this fix.
Checks for SMES Z level at power_failure.dm

Little fix which checks Z level of SMES before drying it up at grid_check event.
Merge pull request #5965 from Lancer411/dev

Fixes for grid_check random event.